UK Coal evacuated one of the nation’s last remaining deep collieries in north Yorkshire after methane gas seeped into the area and ignited.
Work at the site in Kellingley has been suspended until it is safe for the 218 miners to return.
The scare took place last Tuesday, when miners detected high levels of poisonous carbon monoxide, indicating that methane seeping from the waste or the surrounding rock was being ignited by a heat source in the rubble.
After the workers were safely evacuated, UK Coal pumped nitrogen gas into the area to starve it of oxygen to ensure there were no further ignitions.
When the levels of carbon monoxide had dropped, a skilled team walked the length of the coal face to investigate but could not find where the combustion was taking place.
The mine and the mining equipment were not damaged in the incident, the team concluded, and more nitrogen is expected to be pumped into the mine until the problem is resolved.
Doncaster-based UK Coal hopes to reopen the mine by the middle of December, but it estimates the incident will reduce coal production by between 100,000 and 200,000t, which is up to 2.7% of the total 7.3M.t the group aimed to extract in 2010.
However, it is in discussions with unions for mining to continue over Christmas to make up some of the shortfall.
Shares in UK Coal were down 0.7% on Tuesday.
The company is one of the UK’s largest brownfield site property developers as well as the supplier of 15% of all the coal burned in the UK. It operates two other deep mines, at Daw Mill near Coventry and Thoresby in Nottinghamshire.